High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described by Whinfield, et al., in U.S. Pat. No. 2,465,319 and by Pengilly, U.S. Pat. No. 3,047,539. Such polyesters are especially useful to form films and fibers.
More recently, it has been disclosed by Borman and Campbell in U.S. Pat. No. 4,271,063, that if a high molecular weight polyester, a copolymer of ethylene and vinyl acetate and a filler are melt blended and then post-reacted by heating in the solid state, the resultant blend can be molded into articles having a number of improved properties.
It is known that the above mentioned polymeric materials can be used to form layered structures, or laminates, comprised of high molecular weight polyester sheets bonded together with ethylene-vinyl acetate copolymer. These can be prepared by compressing ethylene-vinyl acetate copolymer between sheets of polyester at an elevated temperature for brief periods. The finished article is particularly useful as packaging film. A drawback, however, is the relatively low degree of adhesion between the layers of the structure, with T-peel strengths as measured on an Instron tester of less than 0.5 in.lbs./in..sup.2 being typical.